This invention relates to a method of manufacturing a non-planar formed body, such as a panel of bent or curved form, of particulate thermal insulating material which may be microporous thermal insulating material.
The term xe2x80x98microporousxe2x80x99 is used herein to identify porous or cellular materials in which the ultimate size of the cells or voids is less than the mean free path of an air molecule at NTP, i.e. of the order of 100 nm or smaller. A material which is microporous in this sense will exhibit very low transfer of heat by air conduction (that is collisions between air molecules). Such microporous materials include aerogel, which is a gel in which the liquid phase has been replaced by a gaseous phase in such a way as to avoid the shrinkage which would occur if the gel were dried directly from a liquid. A substantially identical structure can be obtained by controlled precipitation from solution, the temperature and pH being controlled during precipitation to obtain an open lattice precipitate. Other equivalent open lattice structures include pyrogenic (fumed) and electro-thermal types in which the average ultimate particle size is less than 100 nm. Any of these materials, based for example on silica, alumina or other metal oxides, may be used to prepare a composition which is microporous as defined above.
It is known, for example from GB-A-1350661, to make planar formed bodies of panel form by introducing dry particulate insulating material into a porous envelope which is then located between planar dies in a press. The press is operated to effect compaction of the particulate material in the envelope into a planar panel.
EP-A-0470723 is directed to the manufacture of non-planar formed bodies of particulate thermal insulating material. Reference is made to the method of GB-A-1350661 but it is stated that this method is not capable of producing non-planar formed bodies. Accordingly, a method is proposed in which a plane panel of compacted dry particulate insulating material is first formed. The plane panel is then disposed in contact with a covering means, such as glass cloth, between appropriate non-planar dies of a forming press. The press is operated and the panel is moulded by the dies into the desired non-planar form.
This method is disadvantageous in that it requires at least two stages and cracks may form in the panel during moulding of the plane panel into the desired non-planar form.
It is an object of the present invention to provide an economical method of manufacturing non-planar formed bodies of thermal insulating material.
We have found that it is possible to manufacture non-planar formed bodies by compacting particulate insulating material contained in a porous envelope between appropriate non-planar dies in a forming means, such as a press, provided special attention is given to the flow of the particulate insulating material during compaction thereof.
Accordingly, the present invention provides a method of manufacturing a non-planar formed body of particulate thermal insulating material comprising:
introducing particulate insulating material into a porous envelope;
locating the envelope with the particulate insulating material in a forming means; and
operating the forming means such that compaction of the particulate material in the envelope is effected into a body of desired non-planar form, accompanied by a downwardly-directed flow of the particulate material towards at least one edge of the body, to achieve a required density distribution of compacted material in the body.
The particulate thermal insulating material may be microporous thermal insulating material.
The forming means may comprise upper and lower forming dies shaped according to the desired form of the body.
The lower forming die may incorporate an elevated region and at least one peripheral region lower than the elevated region.
The lower forming die may be of elongate arched, humped or convex form. Such a form may be an elongate form corresponding to part of the surface of a cylinder (i.e. curved in one direction and rectilinear in the orthogonal direction), or may be an elongate form having a cross section corresponding substantially to an inverted V.
The upper forming die may be substantially complementary in contour to the lower forming die.
The forming dies may be incorporated in a press.
The downwardly-directed flow of the particulate thermal insulating material during compacting thereof may be towards two opposite edges of the body.
The non-planar formed body may comprise a curved or bent panel.
The porous envelope may comprise glass or ceramic cloth, or textile cloth of organic and/or inorganic material, or metal cloth, or perforated metal or plastics foil.
The invention is now described by way of example with reference to the accompanying drawings in which: